The top of one of President Donald Trump's eight border wall prototypes along US- Mexico border near San Diego, California. Reuters/Mike Blake

The Trump administration unveiled eight prototypes for the US-Mexico border wall in October.

Six companies were commissioned to create four concrete prototypes, and four prototypes made of "other materials."

President Donald Trump is visiting the prototypes on Tuesday. He said he'll choose the one he likes best.

In October, Customs and Border Protection unveiled eight prototypes on for President Donald Trump's long-promised wall along the 1,900-mile US-Mexico border.

On Tuesday, Trump is visiting the prototypes to inspect them for himself. "I'll see you at the wall!" he said as he boarded Marine One on the way to California.

Workers from six companies spent a month constructing prototypes designed to deter illegal entry of immigrants and drugs. Then the tactical teams took over to test each stretch of wall.

They evaluated if the prototypes could prevent breaching, climbing, and digging, as well as ensure the safety of CBP officers, according to Ron Vitiello, CBP's acting deputy commissioner.

Shortly after taking office, Trump issued an executive order demanding that the Homeland Security Secretary "take steps to immediately plan, design and construct a physical wall along the southern border, using appropriate materials and technology to most effectively achieve complete operational control of the southern border."

Although Trump's plans for a border wall have been beset by a number of obstacles — including the Senate's refusal to greenlight a $1.6 billion down payment, Mexico's refusal to pay for it, wavering estimates on the total cost, and a lawsuit from California — his administration has moved ahead with the prototypes.

Here's what they look like:

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The eight prototypes have gone up near the Otay Mesa port of entry in San Diego, California, just across from Tijuana, Mexico.

Four of the prototypes are concrete walls.

The other half are made of "other materials," including steel.

Each of the prototypes were specifically designed to impede digging and climbing, and withstand breaches, Vitiello said Thursday.

Reuters/Jorge Duenes

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Two of the prototypes appear to have the "see-through" component Trump has mentioned in several rallies and interviews. The president has explained that the transparency will allow people on the US side to avoid getting hit by "large sacks of drugs" catapulted over the wall.

Each of the prototypes is between 18 and 30 feet high.

"The biggest impression I have is how big they are," Vitiello told reporters in October.

Reuters/Jorge Duenes

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Construction crews first broke ground on September 26, and wrapped up by the October 26 deadline.

Reuters/Jorge Duenes

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CBP said the prototypes were designed to "deter illegal border crossings." Here's their video of the initial construction phase:

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And here's a time-lapse video of the entire construction period:

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The estimated cost for the eight prototypes is between $2.4 million and $4 million, in total. The Department of Homeland Security has said those funds are being taken from "reprogrammed money" within CBP, and is not part of the down payment funding for the final wall that still has to make it through Congress.

CBP then waited another 30 days for the concrete to set. The tactical teams spent another 30 to 60 days testing the prototypes against breaching equipment, and climbing and digging tools.

Reuters/Mike Blake

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After the testing, Vitiello said CBP would take another 30 to 60 days to evaluate all the material and "develop a new standard" for the wall's design.

Reuters/Mike Blake

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Vitiello told reporters he believes that when barriers such as the border wall prototypes are "effectively resourced," they work. "Recognize that it isn't just concrete and steel — we need to have the sensors, the cameras, the patrol roads, and obviously the agents," he said.

Reuters/Mike Blake

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Trump will inspect the prototypes himself on Tuesday. "I'm gonna go out and look at them personally, and I'm gonna pick the right one," he said at a rally in Alabama on September 22.